In fact, this whole novel is not what you might expect. Fans — and attentive detractors — will easily fill their John Irving bingo cards with the author’s usual motifs and references to his own life, but it’s certainly not one of his ridiculous books, like “The Fourth Hand,” or even one of his tragically flawed ones, like “Last Night in Twisted River.” Instead, the sophisticated and garish elements of “In One Person” are laced together in an act of literary transvestism.

The story is told in retrospect by a man in his late 60s named Billy Abbott. He looks back across the decades to his adolescence in First Sister, Vt., the home of a mid-rate boys academy, where homophobia was practically the school motto. “We are formed by what we desire,” Billy announces, and what he desired followed none of the dorm rules.

As with many of Irving’s bestsellers, the kooky sex scenes here will steal the headlines, but this is a novel feverishly running its fingers down the spines of other books; it’s as packed with allusions to works of literature as Jeffrey Eugenides’s “The Marriage Plot.” Billy says in the opening paragraph, “I became a writer because I read a certain novel by Charles Dickens.” And like Dickens, Irving sets a stage filled with irresistible and sometimes irresistibly bizarre characters.

The first is an “austerely formal” town librarian named Miss Frost with hypnotizing breasts. She becomes one of the inappropriate objects of Billy’s desire and the guide to his literary tastes. Alarmed by the school physician, who claims that homosexual “afflictions” must be treated aggressively, Billy asks Miss Frost if she can recommend “any novels about young people who have . . . dangerous crushes.” She leads him to “Wuthering Heights,” “Jane Eyre,” “Tom Jones” and “Great Expectations,” hardly what the 13-year-old expected, but not as surprising as what she eventually reveals in the basement of the library. (Don’t ask, don’t tell!)

Meanwhile, Billy’s own family is full of more fantastic characters — and literature. His Grandpa Harry is a cross-dressing lumberman who grabs all the best female parts at the local theater. Harry’s Norwegian business partner is also the theater’s tyrannical director, who makes their patrons endure Ibsen as often as possible. And Billy’s handsome new stepfather has just been hired at the local prep school “to beat the boys silly with Shakespeare,” whose plays, of course, were once performed entirely by men and boys.

This wonderful first section of the novel shows what a ringmaster Irving can be. His looping chronology gives the impression of aimless digression only until we catch up and find him on the trail of some larger truth. The story swings confidently from the burlesque comedy of Billy’s dolled-up grandfather to the poignant anxiety of the boy’s sexual confusion. And it’s full of insights about classic theatre and novels, all gracefully integrated into Billy’s struggle to figure out what kind of person he is. Flaubert’s “Madame Bovary” makes him think hard about the costs of violating moral conventions; James Baldwin’s “Giovanni’s Room” opens up other doors. (Oblique references to Irving’s own novels are mercifully few and endearingly humble.)

The most touching episode takes place during rehearsals for “The Tempest,” when Billy is cast as Ariel. The sprite’s mutable gender appeals to him, and he wants “to capture something of Ariel’s unresolved sexuality.” But he’s just beginning to realize how precarious bisexuality is in a society obsessed with taking sides, with labeling, with determining who’s acceptable and who isn’t. “Enter Ariel, invisible,” the stage directions read, as though foreshadowing Billy’s future status with potential partners: His undemarcated desire will render him invisible to straight women, who suspect he’s unreliable, and to gay men, who don’t trust him.

The heart of Irving’s sympathy may stem from the way he frames bisexuality as a metaphor for his own creative life. When Billy’s bitter mother says, “Novels are just another kind of cross-dressing,” she’s clearly touching on the indeterminate nature of the writer’s mind, the omnivorous consciousness needed to inhabit all different kinds of characters. “In One Person” explores that theme along parallel tracks — sexual and textual — to convey just how lonely the novelist’s work can be.

When Billy matures and moves away from the Favorite River Academy, the story grows more melancholy and, frankly, loses some of its drive, too. The forbidden family secrets that haunt Billy are neither forbidden enough nor secret enough to carry the weight they are given. Even more problematic is the way the plot’s structure fades: The town of First Sister is so concrete, so full of elbowing classmates, outrageous relatives and Miss Frost with her perfectly shaped bosom. (No breasts have received so much attention since Philip Roth’s narrator became one.) Once Billy travels to Europe, the narrative begins to float a bit off the ground, skate through the years and lose its wondrous specificity.

Except in the matter of sexual mechanics. We’re used to gonzo scenes of physical engagement in Irving’s fiction, but readers of any orientation may sometimes find the details here a little too well lubricated. It’s hard to avoid the sense that we’re watching a straight man strain to prove his bona fides by strapping on the leather mantle of Edmund White. Too soon that polemic tickle becomes dominant. As an adolescent, Billy’s struggle to understand himself and gain respect for his sexual ambiguity is charming and sweet. As an adult, though, he tends toward righteous pronouncements about gender equality — “pleas for tolerance of sexual difference.” These can sound like rousing applause lines for a speech at the next convention for Gay and Lesbian Affirmative Psychotherapy (“The World According to GLAP”).

What’s vastly more powerful is Irving’s survey of the AIDS crisis in New York during the 1980s. From the start of the novel we know it’s coming, that baffling complex of cancers, fevers and blindness that ravaged the country. Irving has a frightening command of the various ways people sickened during those dark days in St. Vincent’s hospital, and he dramatizes one death after another with such extraordinary compassion that the victims and their families step out from the fog of statistics and take their place as separate tragedies, every one.

The very end of the story, however, is more hopeful. Alas, probably too hopeful, infused with the triumphalism of a very special transgendered episode of “Glee.” Young Billy once claimed that Shakespeare should have stopped “The Tempest” before the epilogue; Irving should have taken that advice. But these are things we can argue about after you’ve read “In One Person,” which you should, particularly as the country lines up for another electoral battle over sexual freedom. No matter what its flaws, there’s a talent at work in this brave new novel that — as Prospero said — “frees all faults.”

Charles is The Post’s fiction editor. You can follow him on Twitter: @RonCharles.

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